In order to satisfy an increasing information and communication amount, an information and communication system having a large capacity and an ultra speed has been required. In a backbone network, a total transmission capacity is expected to reach several hundreds or several terabytes based on a basic transmission amount of tens of gigabyte bands.
Meanwhile, a photodetector having high sensitivity is required even in a receiving unit of a laser radar for a medical use or a 3-dimensional image and in this case, when the photodetector having a high reception is used, good transmission quality and excellent image data can be acquired without using a photoamplifier. Herein, an avalanche photodiode is used as a light receiving element of the photodetector having the high receive sensitivity.
The avalanche photodiode has a complicated structure and a difficult fabricating method and is fabricated so as to have a planar type because of reliability, as compared with a pin photodiode. However, since the avalanche photodiode having the planar type uses a diffusion process in which a p-type impurity is injected into only a patterned portion, a pre-breakdown due to an undesirable junction curvature occurs. In order to solve the problem, a guardring structure is proposed to maintain a high electric field at only the center of a junction region. The guardring structure means a structure in which an region having a small diffusion depth is formed around the junction region in order to prevent a junction breakdown from being easily generated at edge regions of the junction region.
The diffusion depth of an impurity (for example, Zn) is different from an absorbing layer in the guardring structure, such that an impurity diffusion process is to be performed two times. However, the impurity diffusion process has a lack of reproducibility, such that it is difficult to form a desired guardring structure by simply performing the continuous diffusion process twice. In addition, because the diffusion process needs to be performed twice, the manufacturing process is complicated and the manufacturing process efficiency is deteriorated.
Meanwhile, in the manufacturing of the avalanche photodiode, in order to improve reproducibility and reliability, a technology of controlling the diffusion depth of the junction region in the formation of the junction region is proposed in Korean Patent Laid-open Publication No. 10-2010-0065706 (hereinafter, referred to as the related art). The related art improves the reproducibility of recess etching by inserting an etching stop layer 210 between a first amplifying layer 202 and a second amplifying layer 204 and improves the reliability of the manufacturing process by controlling an etching depth (see FIG. 4). However, in the related art, a characteristic of dark current (current flowing even when light is not blazing down) is deteriorated because the etching stop layer 210 made of InGaAs is not removed and remains, such that an electric characteristic of the avalanche photodiode is deteriorated. Further, because the amplifying layers are formed in a double layer, the manufacturing efficiency is deteriorated.